The powertrain control module (PCM) monitors the secondary heated oxygen sensor (secondary HO2S (sensor 2)) circuit for electrical malfunctions. The described circuit check will detect short circuit to ground, short circuit to power, and open circuit failure modes. High voltage is measured for rich lambda, respectively low voltage for lean lambda. The sensor jumps between these two voltages during normal operation. If open circuit or damaged sensor heating element occurs, the voltage falls back to an output 0.45 V. For secondary HO2S (sensor 2), 0.45 V is not a normal operating voltage. For the diagnostics of short circuit to ground and open circuit, a test pulse is generated. This test pulse produces a specific pump current. Based on the pump current, the sensor voltage increases. After turn off, the sensor voltage decreases. In case of high exhaust gas temperature and interrupted ground wire, a coupling of the sensor signal can occur. The detection of this fault is not possible using the common approach, as the secondary HO2S (sensor 2) voltage remains not necessarily in the counter voltage band, but it can be in the plausibly rich voltage range. In this case an internal resistance plausibility check is utilized to detect open circuit fault. If the checked results are implausible, the PCM detects a malfunction and stores a DTC.